Compensated programmable RF attenuator

Abstract

A programmable RF attenuator having a first connection node and a second connection node is disclosed. The programmable RF attenuator provides RF attenuation between the first connection node and the second connection node based on at least a first attenuation control signal. The programmable RF attenuator includes a first RF attenuator circuit and a first reactance compensation circuit, such that the first RF attenuator circuit includes a first shunt transistor element and a first shunt resistive element, which is coupled to the first shunt transistor element. The first shunt transistor element receives the first attenuation control signal. The first reactance compensation circuit is coupled to the first RF attenuator circuit and at least partially compensates for reactive characteristics of the programmable RF attenuator that affect an attenuation flatness of the programmable RF attenuator.

What is claimed is: 
     
       1. A programmable RF attenuator having a first connection node and a second connection node, and comprising:
 a first RF attenuator circuit comprising a first shunt transistor element and a first shunt resistive element, which is coupled to the first shunt transistor element, wherein the first shunt transistor element is configured to receive a first attenuation control signal; and 
 a first reactance compensation circuit coupled across the first shunt resistive element and configured to at least partially compensate for reactive characteristics of the programmable RF attenuator that affect an attenuation flatness of the programmable RF attenuator, wherein the programmable RF attenuator is configured to provide RF attenuation between the first connection node and the second connection node based on at least the first attenuation control signal. 
 
     
     
       2. The programmable RF attenuator of  claim 1  wherein the first reactance compensation circuit comprises a first compensation resistive element and a first compensation capacitive element, such that the first compensation resistive element and the first compensation capacitive element are coupled in series. 
     
     
       3. The programmable RF attenuator of  claim 2  wherein the first RF attenuator circuit is a shunt attenuator circuit, wherein the first reactance compensation circuit is further configured to at least partially compensate for an effective shunt inductance of the first RF attenuator circuit, such that the reactive characteristics of the programmable RF attenuator comprise the effective shunt inductance. 
     
     
       4. The programmable RF attenuator of  claim 1  wherein the first shunt transistor element is configured to operate in one of an ON state and an OFF state based on the first attenuation control signal, such that during the ON state, the first shunt resistive element is configured to provide at least part of the RF attenuation. 
     
     
       5. The programmable RF attenuator of  claim 1  wherein the first RF attenuator circuit further comprises a first series transistor element coupled between the first connection node and the second connection node, such that the first series transistor element is configured to receive a second attenuation control signal. 
     
     
       6. The programmable RF attenuator of  claim 5  wherein the first reactance compensation circuit is further configured to at least partially compensate for an effective series capacitance of the first series transistor element, such that the reactive characteristics of the programmable RF attenuator comprise the effective series capacitance. 
     
     
       7. The programmable RF attenuator of  claim 5  wherein the first series transistor element is configured to operate in one of an ON state and an OFF state based on the second attenuation control signal, such that during the OFF state, the first shunt resistive element is configured to provide at least part of the RF attenuation. 
     
     
       8. The programmable RF attenuator of  claim 5  wherein the first RF attenuator circuit further comprises a second shunt resistive element and a third shunt resistive element; such that the second shunt resistive element is coupled between the first shunt resistive element and a first current-carrying terminal of the first series transistor element, and the third shunt resistive element is coupled between the first shunt resistive element and a second current-carrying terminal of the first series transistor element. 
     
     
       9. The programmable RF attenuator of  claim 5  wherein the first RF attenuator circuit is a Tee attenuator circuit, wherein the first reactance compensation circuit is further configured to at least partially compensate for an effective shunt inductance of the first RF attenuator circuit and at least partially compensate for an effective series capacitance of the first series transistor element, such that the reactive characteristics of the programmable RF attenuator comprise the effective shunt inductance and the effective series capacitance. 
     
     
       10. The programmable RF attenuator of  claim 5  wherein the first RF attenuator circuit further comprises a second shunt resistive element and a second shunt transistor element; such that the first shunt resistive element is coupled between the first shunt transistor element and a first current-carrying terminal of the first series transistor element, and the second shunt resistive element is coupled between the second shunt transistor element and a second current-carrying terminal of the first series transistor element. 
     
     
       11. The programmable RF attenuator of  claim 10  further comprising a second reactance compensation circuit configured to at least partially further compensate for the reactive characteristics of the programmable RF attenuator, wherein the second reactance compensation circuit is coupled across the second shunt resistive element. 
     
     
       12. The programmable RF attenuator of  claim 11  wherein the first RF attenuator circuit is a Pi attenuator circuit, wherein the first reactance compensation circuit is further configured to at least partially compensate for a first effective shunt inductance of the first RF attenuator circuit and the second reactance compensation circuit is configured to at least partially compensate for a second effective shunt inductance of the first RF attenuator circuit. 
     
     
       13. The programmable RF attenuator of  claim 1  further comprising a plurality of RF attenuator circuits and a plurality of reactance compensation circuits, wherein the plurality of RF attenuator circuits is coupled in series between the first connection node and the second connection node; the plurality of RF attenuator circuits comprises the first RF attenuator circuit; the plurality of reactance compensation circuits comprises the first reactance compensation circuit; and each of the plurality of reactance compensation circuits is configured to at least partially compensate for the reactive characteristics of the programmable RF attenuator that affect the attenuation flatness of the programmable RF attenuator. 
     
     
       14. The programmable RF attenuator of  claim 1  further configured to provide variable attenuation, wherein:
 the first shunt transistor element is configured to operate within a first analog operating region; 
 the first attenuation control signal is an analog control signal configured to select an operating point in the first analog operating region; and 
 the first shunt transistor element and the first shunt resistive element are configured to provide at least part of the RF attenuation. 
 
     
     
       15. The programmable RF attenuator of  claim 14  wherein:
 the first RF attenuator circuit further comprises a first series transistor element coupled in series between the first connection node and the second connection node; 
 the first series transistor element is coupled to the first shunt transistor element and is configured to receive a second attenuation control signal; 
 the first series transistor element is configured to operate within a second analog operating region; 
 the second attenuation control signal is an analog control signal configured to select an operating point in the second analog operating region; and 
 the first shunt transistor element, the first shunt resistive element, and the first series transistor element are configured to provide at least a part of the RF attenuation. 
 
     
     
       16. The programmable RF attenuator of  claim 1  configured to:
 receive an RF input signal via the first connection node; and 
 provide an RF output signal via the second connection node based on the RF input signal and the RF attenuation. 
 
     
     
       17. The programmable RF attenuator of  claim 16  wherein control circuitry is configured to provide at least the first attenuation control signal to select a magnitude of the RF attenuation. 
     
     
       18. The programmable RF attenuator of  claim 16  wherein a frequency of the RF input signal is between 10 Megahertz and 40 Gigahertz. 
     
     
       19. The programmable RF attenuator of  claim 1  wherein a monolithic microwave integrated circuit (MMIC) comprises the programmable RF attenuator.